The invention relates to electron multipliers and radiation detectors.
An electron multiplier can be formed by bonding a perforated or porous plate, e.g., a lead glass plate, between an input electrode and an output electrode, and providing a high voltage direct current (DC) field between the electrodes. When incident particles, such as electrons, ions, or photons, strike the input electrode and collide against glass surfaces within the plate, electrons, sometimes called xe2x80x9csecondary electronsxe2x80x9d, are produced. The secondary electrons are accelerated by the DC field toward the output electrode, and collide against other surfaces within the plate to produce more secondary electrons, which can in turn produce more electrons as they accelerate through the plate. As a result, an electron cascade or avalanche can be produced as the secondary electrons accelerate through the plate and collide against more surfaces, with each collision capable of increasing the number of secondary electrons. A relatively strong electron pulse can be detected at an output face.
Electron multipliers commonly include two types of plates: microchannel plates (MCPs) and microsphere plates (MSPs). Microchannel plates (MCPs) typically include a glass plate perforated with a regular, parallel array of microscopic channels, e.g., cylindrical and hollow channels. Each channel, which can serve as an independent electron multiplier, has an inner wall surface formed of a semi-conductive and electron emissive layer. As incident particles enter a channel and collide against the wall surface to produce secondary electrons, a cascade of electrons can be formed as the secondary electrons accelerate along the channel (due to the DC field), and collide against the wall surface farther along the channel, thereby increasing the number of secondary electrons.
Microsphere plates (MSPs) typically include a glass plate formed of microscopic glass spheres that have semi-conductive and electron emissive surfaces. The spheres are packed and bonded together, e.g., by compression and sintering. As incident particles collide against the surfaces of the spheres to form secondary electrons, a cascade of electrons can be formed as the secondary electrons accelerate through the interstices defined by the spheres and collide against the surfaces of other spheres.
The invention relates to electron multipliers and radiation detectors.
In one aspect, the invention features an electron multiplier including a plate having a plurality of interconnected fibers having electron-emissive surfaces.
Embodiments may include one or more of the following features. The fibers include a glass having lead. The fibers include a neutron-sensitive material. The neutron-sensitive material is selected from a group consisting of 6Li, 10B, 155Gd, and 157Gd in excess of their natural abundance. The fibers include a hydrogen-containing material. The fibers have a length to width aspect ratio of about 50:1 to about 3,000:1, although higher aspect ratios are possible. The plate has a void volume percentage between about 25% and about 90%. The fibers have a first region having a first lead concentration, and a second region having a second lead concentration greater than the first lead concentration. The first region is between the second region and the surfaces of the fibers.
In another aspect, the invention features an electron multiplier including a plate having interconnected particles having material selected from a group consisting of 6Li, 10B, 155Gd, 157Gd, in excess of their natural abundance, Pb, and a hydrogen-containing material.
Embodiments may include one or more of the following features. The particles include glass having lead. The glass and the material are intimately mixed. The particles include spheres and/or shards. The particles include a core, e.g., substantially spherical, of the material. The core is surrounded by a layer of glass. The layer of glass includes a neutron-sensitive material selected from a group consisting of 6Li, 10B, 155Gd, and 157Gd in excess of their natural abundance. The material is dispersed within the particles.
In another aspect, the invention features a neutron-sensitive particle including a core having a material selected from a group consisting of 6Li, 10B, 155Gd, 157Gd, in excess of their natural abundance, Pb, and a hydrogen-containing material; and a glass portion surrounding the core.
Embodiments may include one or more of the following features. The core is substantially spherical. The glass portion includes lead. The glass portion has a first region having a first lead concentration, and a second region having a second lead concentration greater than the first lead concentration. The first region is between the second region and an outer surface of the glass portion.
In another aspect, the invention features an electron multiplier including a plate having an array of channels; and a plurality of interconnected particles in at least one channel.
Embodiments may include one or more of the following features. The particles fill a portion of the channel. The plate includes a glass having lead. The particles include fibers, shards, and/or spheres. The particles have an electron-emissive surface layer. The channels have an electron-emissive surface layer. The particles include a neutron-sensitive material selected from a group consisting of 6Li, 10B, 155Gd, and 157Gd in excess of their natural abundance. The particles include a hydrogen-containing material. The particles include a core of the neutron-sensitive material. The core is substantially spherical. The channels have different widths along their lengths. The particles extend flushed to a surface of the plate. The particles further cover at least a portion of a surface of the plate different than a surface of the channel. The multiplier further includes an electrode covering a portion of the plate and the particles.
In another aspect, the invention features an X-ray sensitive particle including a core comprising lead and a glass portion surrounding the core. The glass portion can include lead. The core can be substantially cylindrical or spherical. The particle can be in the form of a fiber, a sphere, or a shard. The particle can be incorporated in multipliers and detectors described herein.
Embodiments may include one or more of the following advantages. The plates can have good mechanical properties, such as relatively good rigidity and/or toughness. The plates can be used in a neutron detector or a neutron imager to provide efficient neutron detection and good spatial resolution, e.g., sub-millimeter resolution. The plates can be used in a hard X-ray ( greater than 10 keV) detector or imager to provide efficient hard X-ray detection and good spatial resolution, e.g., sub-millimeter resolution. The plates can be fabricated into very large area formats, e.g., larger than a square meter. The plates can be curved or shaped to match focal plane requirements.
Other features, aspects, and advantages of the invention are in the description, drawings, and claims.